1. Field of the Invention
The present invention relates to a drive transmission apparatus used in an image forming apparatus represented by a printer, copying machine, facsimile, or the like, an image reading apparatus, or a sheet feeding apparatus of auto document feeder (ADF). Further, the present invention relates to a sheet feeding apparatus provided with a drive transmission apparatus.
2. Description of the Related Art
In a conventional sheet feeding apparatus that separates and conveys loaded sheets, a drive transmission apparatus which includes a planetary gear mechanism (also referred to as a pendulum mechanism) has been used to allow a variety of operations a single drive source.
The planetary gear mechanism includes a sun gear that rotates around a fixed shaft and a planetary gear supported by an arm (also referred to as a pendulum) so that the planetary gear can revolve around the sun gear while being engaged with the sun gear. The arm is supported rotatably around a rotation center of the sun gear.
Since a rotational load is imposed on the arm by a friction member or the like from the planetary gear, when the sun gear is rotated by the drive source, the arm rotates before the planetary gear rotates. Thus, the planetary gear revolves around the sun gear and when, as a result, the planetary gear is engaged with another driven gear and rotational movement of the arm is blocked, the planetary gear starts to rotate. Then, the driving is transmitted from the driven gear further to another gear train.
If the sun gear is rotated in an opposite direction by the drive source, the arm rotationally moves in a direction that moves the planetary gear away from the driven gear to separate the planetary gear from the driven gear, so that drive transmission is released.
To transmit a reverse rotation to a drive train downstream from the driven gear while maintaining an engaged state of the planetary gear and the driven gear, a method for forcibly locking the arm (see, for example, Japanese Patent Application Laid-Open No. 2007-284214) by adding another driving member such as a solenoid has frequently been used.
However, the above method for forcibly locking the arm by adding another driving member such as a solenoid as discussed in Japanese Patent Application Laid-Open No. 2007-284214 has a problem that manufacturing costs increase with addition of expensive parts, which is to be addressed.